Method for drying ammonium nitrate and like materials



p 1953 E. EDMUNDS, JR 2,653,391

METHOD FOR DRYING AMMONIUM NITRATE AND LIKE MATERIALS 7 Filed Feb. 1, 1951 AIR AIR NH NO n 4 3 5 STEAM 6 i 3 i 1-. I I 8 4 g l I i I 7 AIR WASH A PREDRYER-7IH7- DRYING HEATER 2o 5 AIR #TRAP AIR 29 t 36 27 as I 1 3| STEAM 26 i 5 2s 24 E 34 AIR 2 AIR .5. WASH I DRYER iH--7 DRY|NG DRYER K30 \4O 37 AIR 22 32 TRAP AIR AIR 35 4| WASH COOLER DRY NH4NO3 INVENTOR. E EDMUNDS,JR.

MMM

A TTORNEVS Patented Se t, 29, 1953 METHOD FQRDRYINGAMMONIUM. NITRATE AND LIKEI MATERIALS.-

Edward Edmundg, J12, Albuquerque,,N; Mex., as signor'to Phillips Petroleum Company, a-corpo rationofDelaware Applicationliebruary, 1, 1951,,Serial1N0. 208,923

1 claim;

This, invention relates to the automatic. con.- trolling of the drying. temperature and dryin rate of material. In one of, its preferred embodiinents my invention relates to the automatic controlling of the drying temperature and drying rate of ammonium nitrate.

In the preparation of various materials, the desired product often contains Water which must be removed before the product is marketed. The removal of Water from some materials, for example ammonium nitrateris particularly desirable since such materials cake or ball when stored with the water contained in them. Thusa drying process is a necessary operation in. the prep aration of. such materials.

For economical reasons, it is desirable to carry out such a drying-process at the maximum possiblerate and temperature- However, if the drying process for such materials is carried out at too high a temperature or too fast, the material may be changed. to an undesirable form or com-'- position. Thus in a drying process of thetype mentioned the object is to dry the material. as rapidly as possible without undesirably altering its form or composition.

In order to accomplish this objective, the dry= ing' temperature and drying rate must be very closely controlled. In the past, such control has been attempted by utilizing manual methods of control inthe drying process. Of course such a procedure has been unsatisfactory due to over= correctingand lag in applying corrections in an attempt to accomplish the degree of control necessary= Such ove'rcorrections and lag in applying corrections cause an undesirable slowing of the drying process oran undesirable change in the product or both. In theprefp'aration of'solid ammoniumnitr-ate, the product-exists asgranule ammonium nitrate containing water. For the reasons previously mentioned this water must be removed by subject'ing the ammonium nitrate to a drying process. It is desirable to retain this granule form and yet carry out the drying process as rapidly as possible. If the process is carried out at too high a temperature or too fast, th'e granules split and undesirable fine, particles result.

By the practice of. my invention, the drying temperature and drying rate, of material are closely and automatically controlled by. automatically controlling the temperature of the drying agentboth before and. after contactof said drying agent with. the material being dried,.thereby permitting the drying process to be carried out a't'the maximum rate withoutundesirab'ly chang- 2. ingtheform. or composition. ofthe material being dried.

An. object of my invention is to control closely the drying temperature and drying rate of material, for example, ammonium nitrate.

Another object is to provide a simple, economic and. dependable method of closely and automati'cally controlling the drying temperature and drying rate of. material, for example, ammonium nitrate..

Another object is to provide the close control necessary in, a drying process to carry the prim ess out at themaximurn speed without undesir= ablyal'tering the material being'dried.

Still another object of my invention is to automatically control the temperature ofthe drying agent before and after contact with the material being dried.

From. the discussion and disclosure herein made, other objects willbe apparent to one skilled in the art.

According to my invention, the temperature of a fluid drying agent is automatically controlled; by suitable means, before andafter contact with the materialbeing dried, thereby closely-and automatically controllingthe temperature and rate of drying; By practicing my invention in the drying process of material, for example ammoniurn nitrate, the drying process may becarri'e'd' out: at the maximum rate possible Without undesirably altering the material being dried.

One; preferred embodiment of my invention is indicated in the attached drawing which is a how sheet of adrying process illustrating a practice of my invention as applied'to ammonium nitrate as the material being dried and air as the drying agent. The individual apparatus and control instruments are well. known in operation and design. From the following discussion and disclosure, it will be clear to one skilled in the art that the practice of my invention is not necessarilylimited to the exact type andv location. of the control. instruments shown nor to the materialsand-conditionsof operation utilized forpurpose of illustration.

'In-the figure, the ammonium: nitrate or other material. to be. dried. is fed: by conveyor belt 3 into in'clined:rotating. predryer 2 the drying air being fed into predryer 2.. by entering drying air line. 1 through air heater s. The air is heated to the. desired initial. temperature by'air heater 4. and, maintained at that temperature by temperature recorder, controller ii. The temperature controller. H. has a. bulb. or other temperature measuringhdevice Ill located in drying air line '3 between air heater 4 and predryer 2 and operating diaphragm valve 6 in steam line 8 by the air furnished by instrument air supply line 63 in known manner. The drying air is drawn from predryer 2 through exit drying air line and passed through air washer [2 by exhaust fan I l and vented into the atmosphere through vent it. The rate of flow of the drying air through predryer 2 is controlled in accordance with my invention by temperature recorder controller it. The temperature recorder controller I t has a bulb or other temperature measuring device Zll in exit drying air line 5 between predryer 2 and air washer is and operating damper l8 located in vent it through diaphragm motor [9 by air furnished by instrument air supply line ll.

The predried ammonium nitrate from predryer 2 is then gravity fed into inclined rotating dryer 22. The drying air is fed into dryer 22 by entering drying air line 23 through air heater 24. The drying air is maintained at the selected initial temperature by temperature recorder controller 2!, the temperature controller having a bulb or other temperature measuring device 36 in drying air line 23 between air heater 24 and dryer 22. Temperature controller 12! operates diaphragm valve 26 in steam line 28 by the air furnished by instrument air supply line 25. The drying air is drawn from dryer 22 in exit drying air line 31 through air washer 32 by exhaust fan 34 and vented into the atmosphere through vent 365. The rate of flow of drying air through dryer 22 is controlled by temperature recorder controller 27, which has a bulb or other temperature measuring device fit) in exit drying air line 31 between dryer 22 and air washer 32. Temperature controller 21 operates damper 38 in vent 38 through diaphragm motor 3! by air furnished by instrument air supply line 29.

The dried ammonium nitrate from dryer 22 is gravity fed into inclined rotating cooler 42. The cooling air is fed into cooler 12 by entering cooling air line i"! through air heater 44. It is understood that in certain cases the temperature of the air may be such that the air must be cooled instead of heated before being passed to cooler 42. In such a case, 44 becomes an air cooler is and steam line at becomes coolant line 458. The cooling air is maintained at the selected initial temperature by temperature recorder controller 33 operating diaphragm valve 46 in steam line d8 by air supplied by instrument air supply line 35. The bulb or temperature measuring device 5G for temperature recorder controller 33 is located in cooling air line ll between air heater it and cooler 42. The exit cooling air is drawn from cooler 42 in exit cooling air line 45 by exhaust fan 54 through air washer 52 and vented into the atmosphere through vent 56. The rate of flow of cooling air through cooler 52 is controlled by temperature recorder controller 39 by operating damper 58 through diaphragm motor 23 by air furnished by instrument air supply line ll. The bulb or other temperature measuring device fill for temperature recorder controller 33 is located in exit cooling air line 35 between cooler 42 and air washer 52.

In the practice of my invention, using as an example ammonium nitrate as the material to be dried and air as the drying agent, and referring to the attached drawing, if the entering drying air in line 2, as measured by bulb Hi, falls below a selected initial temperature, the air pressure exerted on diaphragm valve 6 through instrument air supply line [3 is changed by temperature recorder controller II. The

change of pressure opens further the valve in steam line 8 allowing more steam to pass through air heater 4 thereby returning the temperature of the entering drying air to the selected value. If the temperature of the entering drying air rises above the selected value, the air pressure from instrument air supply line i3 to diaphragm valve 6 is changed by temperature recorder con troller I! such that diaphragm valve 6 reduces the flow of steam in steam line 8 to air heater 4, thereby allowing the temperature of the entering air to return to the selected value. Thus the drying temperature of the ammonium nitrate is automatically controlled.

If the drying air temperature leaving predryer 2 through exit drying air line 5 falls below a selected value, as measured by bulb 20, indicating too slow a drying rate, the air pressure exerted on diaphragm motor l9 through instrument air supply line i! is changed by temperature recorder controller 15. The change in pressure on diaphragm motor l9 moves damper it? toward an open position in vent Iii allowing the rate of flow of air through predryer 2 to increase thus increasing the rate of drying in predryer 2. As the rate of flow of air increases, the rate of drying increases and the temperature of the exit drying air rises to the selected value. If the temperature of the exit air rises above the selected value indicating too fast a drying rate, the air pressure from instrument air supply line i? to diaphragm motor I 9 is changed by temperature recorder controller [5 such that diaphragm motor 19 moves damper 18 toward a closed position. 'The closing of damper 18 reduces the rate of flow of air through predryer 2 thereby decreasing the drying rate. As the rate of flow of air through predryer 2 decreases, the rate of drying decreases and the temperature of the exit drying air falls to the selected value.

If the air leaving cooler 42 through exit line t5, as measured by bulb Ell, falls below the selected value indicating insufficient cooling, the air pressure exerted on diaphragm motor 53 through instrument air supply line ll is changed by temperature recorder controller 39. The change in pressure on diaphragm motor 43 turns damper 58 toward a closed position in vent 56 thus decreasing the flow of air through cooler 22. Decreasing the flow of air through cooler 42 increases the extent of cooling and returns the temperature to the selected value. If the exit air temperature rises above the selected value, indicating excess cooling, the air pressure from instrument air supply line 4| to diaphragm motor 43 is changed by temperature recorder controller 39 such that diaphragm motor 43 moves damper 58 in vent 56 toward an open position thus increasing the flow of air through cooler 42. Increasing the flow of air through cooler 42 decreases the extent of cooling and returns the temperature to the selected value.

Although my invention is primarily directed at controlling the rate and temperature of drying, it will be apparent to one skilled in the art, after reading the disclosure of my invention herein made, that the practice of my invention is equally advantageous in a cooling process as is indicated in the example and disclosures herein given. Thus although the language of the disclosure and claims herein made speaks primarily in terms of controlling drying temperatures and rates, I intend that the disclosure and claims of my invention include cooling operations as well as drying operations that may occur in a drying process.

As the temperature and rate of drying must be closely controlled in each stage of the drying of ammonium nitrate, my invention can be advantageously practiced in any or all of the various ammonium nitrate drying stages.

Example In a preferred embodiment of my invention, ammonium nitrate was dried by air in three stages. 7

Referring to the figure, 26,000 pounds per hour of granule ammonium nitrate from a prilling tower were continuously fed into predryer 2 by conveyor belt 3. The feed ammonium nitrate was at a temperature of 75 C. and contained 4 weight per cent water. The predried ammonium nitrate leaving predryer 2 was at a temperature of 65 C. and contained 2.75 per cent water. The drying air entering predryer 2 was kept at 75 C. by temperature recorder controller H. The drying air left predryer 2 at an average rate of 22,000 cubic feet per minute and contained 3.8 per cent water. The temperature of the exit drying air was kept at 65 C. by temperature recorder controller I5.

The predried ammonium nitrate at 65 C. containing 2.75 per cent water was gravity fed into dryer 22. The dried ammonium nitrate left the dryer at 80 C. and contained 0.5 per cent water and was gravity fed into cooler 42. The drying air entering dryer 22 was kept at 145 C. by temperature recorder controller 2|. The drying air left the dryer at an average rate of 11,000 cubic feet per minute and contained 5.7 per cent Water. The temperature of the exit drying air from dryer 22 was kept at 75 C. by temperature recorder controller 21.

The dried ammonium nitrate entered cooler 42 at 80 C. and 0.5 per cent water content and left the cooler at a rate of 25,000 pounds per hour at 38 C. and contained 0.3 per cent water. The cooled ammonium nitrate was further treated to prevent absorbing of moisture. The air entering cooler 42 was kept at 21 C. by temperature recorder controller 33. The air left cooler 42 at an average rate of 27,400 cubic feet per minute and contained 2.9 per cent water. The temperature of the exit air was kept at 37 C. by temperature recorder controller 39.

The foregoing example was directed toammonium nitrate as the material being dried and air as the drying agent, however other materials such as corn germ, clay, potassium nitrate, cereals, coal, etc. can be dried by the process and apparatus of my invention and also drying agents other than air such as combustion gases resulting from burning gas, oil, coal etc., are suitable for the practice of my invention.

Since various details of construction, locations of instruments, types of instruments utilized for measurements and control, materials to be dried, and drying agents may be utilized in the practice of my invention, I do not desire to be limited to the single embodiment and illustrations as herein disclosed.

I claim:

As a method for drying granule ammonium nitrate containing water a three stage process which comprises a predrying stage, a drying stage and a cooling stage, with the temperature of drying air in each stage being automatically controlled before contact with said granule ammonium nitrate, and with the rate of flow of said drying air past said granule ammonium nitrate being regulated automatically in each stage by controlling the temperature of said drying air after contact with said granule ammonium nitrate automatically in response to and to compensate for any variation, and wherein the temperature of said drying air before contact with said granule ammonium nitrate is maintained at 75 C. in said predrying stage, 145 C. in said C. in said cooling stage, and

drying stage, and 21 wherein the temperature of said drying air after contact with said granule ammonium nitrate is maintained at C. in said predrying stage, C. in said drying stage, and 37 C. in said cooling stage, and wherein said granule ammonium nitrate is introduced into said predrying stage at a temperature of 75 C. and containing 3.5 to 4.5 weight per cent water, and wherein said granule ammonium nitrate is withdrawn from said into said drying stage at a temperature of 65 C. and containing substantially 2.75 weight per cent water, and wherein said granule ammonium nitrate is withdrawn from said drying stage and. introduced into said cooling stage at a temperature of C. and containing substantially 0.5 weight per cent water, and wherein said granule ammonium nitrate is withdrawn from said cooling stage at a temperature of 38 C. and containing substantially 0.3 weight per cent water.

EDWARD EDMUNDS, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 545,120 Cummer Aug. 27', 1895 748,525 Perry et al. Dec. 29, 1903 1,312,759 Stacey,'Jr. Aug. 12, 1919 1,676,786 Lissauer July 10, 1928 1,729,424 Harshow et al. Sept. 24, 1929 1,750,813 Oakley et al. Mar. 18, 1930 2,402,192 Williams et al. June 18, 1946 2,5 5 Erisman et al Oct. 10, 1950 OTHER- REFERENCES Serial No. 405,274, Van Aken, (A. P. 0.), published May 4, 1943.

The Link-Belt Roto-Louvre Dryer. Book No. 1911, The Link-Belt Company, Chicago, Illinois; pages 5, 7, 15, 18 and 19 relied on.

predrying stage and introduced 

